The present invention relates to a column-and-beam join structure having a vibration-mitigating property in a steel frame when a steel structure building is constructed and, more specifically, to a column-and-beam join structure capable of absorbing the energy of an earthquake by split tees yielding before the column and the beam in a column-and-beam join structure which is made of a steel column and a steel beam using split tees.
In a column-and-beam join structure according to the present invention, the steel column includes not only an H-shaped steel column or a square steel tube column but also a column of any cross-sectional shape which may be connected using split tees, and the steel beam includes not only an H-shaped steel beam but also a section beam of an L-shape, a T-shape, or another shape in cross section, which may be connected using split tees.
When a steel column and a steel beam are connected in a steel structure building, there are cases where split tees of, for example, a T-shape (or an L-shape) are used. In such a column-and-beam join structure, in order to form a final collapse system at the time of a large earthquake or the like, when a square steel tube column is used as a steel column, the column-and-beam join structure is generally designed so as to cause the column to yield by applying a bending deformation, such as bulging or concaving a side wall of the column to which split tees are connected in accordance with a tension or a compression imposed thereon from the portion to which the beam is connected. However, since the flexural strength of the flanges of the split tees is critical in design, the thickness and width of the flanges must be increased in order to sufficiently secure the rigidity and proof stress of the flanges, and therefore it is not economical.
Further, in Japanese Unexamined Patent Publication No. H11-229493 or H7-102635, as shown in FIGS. 19 and 20, a column-and-beam join structure is proposed wherein: an H-shaped steel column 1a(1) is used as a steel column 1; the flanges 5 of a pair of upper and lower split tees 4 are connected to a flange 2 of the H-shaped steel column 1a(1) using bolts 3; the end portions 8a of both the upper and lower flanges 8 of an H-shaped steel beam 7 used as a steel beam are assembled between the webs 6 of both the upper and lower split tees 4 and are connected to the webs 6 using bolts 9. In such a column-and-beam join structure, as shown in FIG. 21, if a tension F, which is imposed from the join portion of a flange 8 of the H-shaped steel beam 7, is applied to the flange 5 of a split tee 4: the flange 5 undergoes bending deformation while bulging so as to separate from the face of a flange 2 of the H-shaped steel column 1a(1); with the bending deformation of the flange 5, the bolts 3 used for connecting the flange 5 to the flange 2 of the H-shaped steel column 1a(1) undergo a bending tension as shown in FIG. 21; the bolts 3 are prized, twisted and cut by the prying action; and thus the tension rupture of the bolts 3 constitutes a final collapse system. In such a case of the tension rupture of bolts as stated above, the column is sometimes damaged by the tension.
On the other hand, in the case of designing a final collapse system for a large earthquake or the like, it is not desirable to make the join portions of a steel column and split tees rupture, and therefore it is an original technique to design the system so as to impose all cross-sectional proof stress on a steel beam so that the rupture may occur in the steel beam itself. However, the yield stress itself of a steel material used for a beam is controlled with only the lower limit of the yield stress. Therefore, even though a system is designed so as to impose all cross-sectional proof stress on a beam, since there are cases where the proof stress of the beam is excessively large, the rupture may occur in bolts, split tees or the portion to which a column is connected, which have no allowance in proof stress, as a result.
Considering the absorption of earthquake energy by a column-and-beam join portion based on the above discussion, in the case where a rupture occurs by the bending deformation of the flange of a split tee, even though the flange bulges for example, the flange sticks closely to the join face of a column finally and therefore the tension and the compression do not become symmetrical and, in the case where a rupture occurs by the tension rupture of bolts, a gap is gradually generated between the face of a column and the face of the flange of the split tee where they are connected by bolts and therefore both loops of tension and compression cannot be obtained when the bolts are plasticized, and, in either of the cases, the deformation develops in one direction and therefore the present situation is that, though the present technique can cope with the design on the proof stress of the split tee, the design of the split tee is not a design capable of coping with the absorption of earthquake energy.
Japanese Unexamined Patent Publication No. 2001-32369 discloses a technology wherein the flange of a split tee is used as an energy absorbing member by making the bending yield of the flange of the split tee precede the tension yield of bolts. However, in the case where the web of a split tee undergoes tension, this technology is effective, but, in the case where the web undergoes compression, energy absorption cannot be expected and, therefore, there is a room for further improvement.
Further, there presently is a column-and-beam join structure constructed by directly welding the ends of both the upper and lower flanges of an H-shaped steel beam to a steel column. However, such conventional method has a drawback of generating a rupture caused by the welding portion of a steel column and an H-shaped steel beam becoming a critical portion.
Thus, at present, in order to prevent a rupture at a weld portion of a steel column and an H-shaped steel beam, as disclosed in Japanese Unexamined Patent Publication No. H8-4112 for example, notches are formed on both sides adjacent to the edges of both the upper and lower flanges of an H-shaped steel beam which is directly welded to a steel column and, by so doing, the portions having the function of absorbing earthquake energy are provided, so that the portions of the H-shaped steel beam except the portions which are welded to the steel column can yield positively. However, when the portions having the function of absorbing earthquake energy are ruptured by a large earthquake or the like and the portions cannot be reused, as the portions having the function of absorbing earthquake energy are welded to the steel column and it is basically impossible to replace the portions having the function of absorbing earthquake energy after the rapture. Therefore, in reality, the steel structure building has to be reconstructed even though the H-shaped steel beam is not ruptured.
In the meantime, disclosed in Japanese Unexamined Patent Publication No. 2000-192547 is a column-and-beam join structure which is provided with an energy absorbing function by reinforcing the end of the lower flange of an H-shaped steel beam which is welded to a steel column via a diaphragm with a beam supporting reinforcing member which is composed of extra mild steel and welded to the steel column, and disclosed in Japanese Unexamined Patent Publication No. H8-151686 is a column-and-beam join structure which is provided with an energy absorbing function by welding ribs composed of a metal material having a lower yield stress than that of a material used for a column or a beam to both the upper and lower flanges of an H-shaped steel beam and by rigidly connecting the steel column to the H-shaped steel beam via the upper and lower ribs. However, when a beam supporting reinforcing member or a portion having an energy absorbing function is ruptured by a large earthquake or the like and becomes hardly reusable, it is impossible to replace the relevant portion only.
The present invention is accomplished in view of the drawbacks of the existing technologies as stated above, and the object thereof is: to provide a column-and-beam join structure capable of plasticizing split tees in advance of a steel beam or a steel column by using split tees which can secure energy absorption without welding the join portions of a steel column and a steel beam and further by granting an energy absorbing function to the webs of the split tees, which are connected to the steel beam using bolts, or to the flanges of the split tees, which are connected to the steel column using bolts, so that the energy caused by a large earthquake or the like can efficiently be absorbed; and further to provide a column-and-beam join structure wherein the replacement and reconstruction of a steel column or a steel beam, which have been required up to now, are not required by making it easier to replace only the split tees which are not reusable due to a large earthquake.
The present invention is accomplished aiming at the above object and is constructed as follows:
The first invention is a column-and-beam join structure fabricated by connecting the flanges of split tees to a steel column using bolts and by engaging and connecting the webs of the split tees to the ends of the flanges of a steel beam using bolts, characterized by making either one or both of the web and the flange of a split tee yield in advance of the column or the beam.
The second invention is a column-and-beam join structure fabricated by connecting the flanges of split tees to a steel column using bolts and by engaging and connecting the webs of the split tees to the ends of the flanges of a steel beam using bolts, characterized in that the upper limit of the yield stress of the steel material used for either one or both of the web and the flange of a split tee is defined to be not more than twice the lower limit thereof.
The third invention is a column-and-beam join structure fabricated by connecting the flanges of split tees to a steel column using bolts and by engaging and connecting the webs of the split tees to the ends of the flanges of a steel beam using bolts, characterized in that a split tee has a shape wherein the cross-sectional area of the web is partially reduced so as to divide the base end portion of the web, the web extending from the flange of a split tee in the axial direction of the steel beam material, from the tip portion thereof to which a flange of the H-shaped steel beam is connected using bolts.
The fourth invention is a column-and-beam join structure according to the third invention, characterized in that the upper limit of the yield stress of the steel material used for the web of a split tee at the portion where the cross-sectional area is partially reduced is defined to be not more than twice the lower limit thereof.
The fifth invention is a column-and-beam join structure according to the third or fourth invention, characterized by placing the web, including the portion where the cross-sectional area of the web of a split tee is partially reduced, between a flange of the steel beam and a section steel for buckling restraint, and connecting the web to them using bolts.
The sixth invention is a column-and-beam join structure according to any one of the first to fourth inventions, characterized by providing reinforcing plates, which protrude in the direction of the web and not touching the web, to both the side edges of the flange of a split tee.
The seventh invention is a column-and-beam join structure according to the third or fourth invention, characterized by: providing reinforcing plates, which protrude in the direction of the web but do not touch the web, to both the side edges of the flange of a split tee; and placing the web, including the portion where the cross-sectional area of the web of a split tee is partially reduced, between a flange of the steel beam and a section steel for buckling restraint, and connecting the web to them using bolts.
The eighth invention is a column-and-beam join structure fabricated by connecting the flanges of split tees to a steel column using bolts and by engaging and connecting the webs of the split tees to the ends of the flanges of a steel beam using bolts, characterized in that: the upper limit of the yield stress of the steel material used for either one or both of the web and the flange of a split tee is defined to be not more than twice the lower limit thereof; and, at a portion where both ends of the flange of the split tee are connected to the steel column using bolts, space keeping members are inserted between the flange of the split tee and the steel column and the flange of the split tee and the steel column are connected in the state of maintaining the space.
The ninth invention is a column-and-beam join structure according to the eighth invention, characterized in that a split tee has a shape wherein the cross-sectional area of the flange is partially reduced.
The tenth invention is a column-and-beam join structure fabricated by connecting the flanges of a pair of upper and lower split tees to a steel column using bolts, by engaging and connecting both the upper and lower flanges of a steel beam between the webs of both the upper and lower split tees using bolts, and by molding a concrete slab to either one of both the upper and lower flanges of the steel beam, characterized in that: the yield stress of the steel material used for the web of the split tee, to which the flange of the steel beam where the concrete slab has been molded is connected, is defined to be higher than the upper limit of the yield stress of the steel material used for the web of the other split tee; and the upper limit of the yield stress of the steel material used for the web of the other split tee is defined to be not more than twice the lower limit thereof.
The eleventh invention is a column-and-beam join structure according to the tenth invention, characterized in that the other split tee has a shape wherein the cross-sectional area of the web is partially reduced.
The twelfth invention is a column-and-beam join structure fabricated by connecting the flanges of a pair of upper and lower split tees to a steel column using bolts and by engaging and connecting both the upper and lower flanges of a steel beam between the webs of both the upper and lower split tees using bolts, characterized in that: one of the upper and lower split tees has a shape wherein the cross-sectional area of the web is partially reduced and the upper limit of the yield stress of the steel material used for the web is defined to be not more than twice the lower limit thereof; and the yield stress of the steel material used for the web of the other of the upper and lower split tees is defined to be higher than the upper limit of the yield stress of the steel material used for the web of the former split tee.
The thirteenth invention is a column-and-beam join structure according to the eleventh or twelfth invention, characterized by placing the web, including the portion where the cross-sectional area of the web of a split tee is partially reduced, between a flange of the steel beam and a section steel for buckling restraint, and connecting the web to them using bolts
The fourteenth invention is a column-and-beam join structure fabricated by connecting the flanges of a pair of upper and lower split tees to a steel column using bolts, by engaging and connecting both the upper and lower flanges of a steel beam between the webs of both the upper and lower split tees using bolts, and by molding a concrete slab to either one of both the upper and lower flanges of the steel beam, characterized in that: the yield stress of the steel material used for the flange of the split tee, to which the flange of the steel beam where the concrete slab has been molded is connected, is defined to be higher than the upper limit of the yield stress of the steel material used for the flange of the other split tee; the upper limit of the yield stress of the steel material used for the flange of the other split tee is defined to be not more than twice the lower limit thereof; and, at a portion where both ends of the flange of the other split tee are connected to the steel column using bolts, space keeping members are inserted between the flange of the split tee and the steel column and the flange of the split tee and the steel column are connected in the state of maintaining the space.
The fifteenth invention is a column-and-beam join structure according to the thirteenth invention, characterized in that the other split tee has a shape wherein the cross-sectional area of the flange is partially reduced.
The sixteenth invention is a column-and-beam join structure fabricated by connecting the flanges of a pair of upper and lower split tees to a steel column using bolts and by engaging and connecting both the upper and lower flanges of a steel beam between the webs of both the upper and lower split tees using bolts, characterized in that: the upper limit of the yield stress of the steel material used for the flange of one of the upper and lower split tees is defined to be not more than twice the lower limit thereof; at a portion where both ends of the flange of the split tee are connected to the steel column using bolts, space keeping members are inserted between the flange of the split tee and the steel column and the flange of the split tee and the steel column are connected in the state of maintaining the space; and the yield stress of the steel material used for the flange of the other of the upper and lower split tees is defined to be higher than the upper limit of the yield stress of the steel material used for the flange of the former split tee.
The seventeenth invention is a column-and-beam join structure according to the sixteenth invention, characterized in that the former split tee has a shape wherein the cross-sectional area of the flange is partially reduced.
By the first invention, as at least one or both of the web and the flange of a split tee is plasticized in advance of a column and a beam, the split tee can absorb energy and also the rotation angle of the beam end can be quantified By so doing, the response reduction effect against an earthquake, a wind or the like can surely be enhanced and a collapse at an undesirable portion, such as the tension rupture of a bolt which has occurred up to now, can be prevented.
By the second invention, as the plasticization of the web portion of a split tee can surely precede that of a column and a beam, the web portion can absorb energy and also the rotation angle of the beam end can be quantified. By so doing, the response reduction effect against an earthquake, a wind or the like can surely be enhanced and a collapse at an undesirable portion, such as the tension rupture of a bolt which has occurred up to now, can be prevented.
By the third or fourth invention, as the plasticization of the web portion of a split tee can precede that of the other portions more surely than in the case of the second invention, the web portion can absorb energy and also the rotation angle of the beam end can be quantified. By so doing, the response reduction effect against an earthquake, a wind or the like can surely be enhanced and a collapse at an undesirable portion, such as the tension rupture of a bolt which has occurred up to now, can be prevented.
By the fifth invention, the portion where the cross-sectional area of the web of a split tee is reduced is reinforced and, when a tension and a compression are imposed on the web, the portion where the cross-sectional area of the web is reduced can be prevented from buckling locally in an off-plate direction on the compression side.
By the sixth invention, as the flange portion of a split tee is reinforced and the bending yield of the flange which has occurred up to now can be prevented, the plasticization of the web portion can precede that of the other portions more surely.
By the seventh invention, as the flange portion of a split tee is reinforced and the portion where the cross-sectional area of the web of the split tee is partially reduced is also reinforced, the bending yield of the flange is prevented and the plasticization of the web portion can precede that of the other portions and also, when a tension and a compression are imposed on the web, the portion where the cross-sectional area of the web is reduced can be prevented from buckling locally in an off-plate direction on the compression side.
By the eighth or ninth invention, as a space is formed between the flange of a split tee and a steel column at the center portion of the flange, even when an excessive stress is imposed in the direction where the web of the split tee is compressed, the energy can be absorbed by the split tee and the column is not damaged. Further, as the plasticization of the flange of the split tee can precede that of the other portions, the energy can be absorbed at the flange portion and also the rotation angle of the beam end can be quantified.
By so doing, the response reduction effect against an earthquake or a wind can be enhanced and a collapse at an undesirable portion, such as the tension rupture of a bolt, can be prevented.
By the tenth or eleventh invention, the rigidity of the flange side of an H-shaped steel beam, to which a concrete slab is molded, is enhanced, the center axis of the H-shaped steel beam moves toward the side to which the concrete slab is molded and, when a tension is imposed on the H-shaped steel beam, as the end of the H-shaped steel beam rotates around a center axis located in the vicinity of the web portion of the split tee which is connected using bolts to the flange side to which the concrete slab is molded, the split tee on the side to which the concrete slab is molded is not plasticized and the web portion of the other split tee to which the concrete slab is not molded is plasticized in advance of the other portions, and, therefore, a usual split tee can be used as the split tee on the side to which the concrete slab is molded. By so doing, since it becomes possible to replace only the other split tee which has become unusable due to a large earthquake or the like, the recovery work can be carried out simply and easily.
By the twelfth invention, a split tee located at one of the upper and lower column-and-beam join portions, which join portion is configured by using the split tee wherein the upper limit of the yield stress of the steel material used for the web is specified in a specific range and the web has a portion where the cross-sectional area of the web is partially reduced, yields in advance of the other split tee located at the other of the upper and lower column-and-beam join portions, which join portion is configured by using the split tee wherein the yield stress of the steel material used for the web is defined to be higher than the upper limit of the yield stress of the steel material used for the web of the former split tee. Therefore, the damage caused by the energy of an earthquake is concentrated on the former split tee. After the earthquake, the earthquake resistance of the building can easily be recovered by replacing the damaged split tee.
By the thirteenth invention, the portion where the cross-sectional area of the web of a split tee is reduced is reinforced and, when a tension and a compression are imposed on the web, the portion where the cross-sectional area of the web is reduced can be prevented from buckling locally in an off-plate direction on the compression side.
By the fourteenth or fifteenth invention, the rigidity of the flange side of a steel beam (H-shaped steel beam), to which a concrete slab is molded, is enhanced, the center axis of the steel beam moves toward the side to which the concrete slab is molded and, when a tension is imposed on the steel beam, as the end of the steel beam rotates around a center axis located in the vicinity of the flange portion of the split tee which is connected using bolts to the flange side to which the concrete slab is molded, the split tee on the side to which the concrete slab is molded is not plasticized and the flange portion of the other split tee to which the concrete slab is not molded is plasticized in advance of the other portions, and therefore a usual split tee can be used as the split tee on the side to which the concrete slab is molded. By so doing, since it becomes possible to replace only the other split tee which has become unusable caused by a large earthquake or the like, the recovery work can be carried out simply and easily.
By the sixteenth or seventeenth invention, a split tee located at one of the upper and lower column-and-beam join portions, which join portion is configured by using the split tee wherein the upper limit of the yield stress of the steel material used for the flange is specified in a specific range and the flange has a portion where the cross-sectional area of the flange is partially reduced, yields in advance of the other split tee located at the other of the upper and lower column-and-beam join portions, which join portion is configured by using the split tee wherein the yield stress of the steel material used for the flange is defined to be higher than the upper limit of the yield stress of the steel material used for the flange of the former split tee. Therefore, the damage caused by the energy of an earthquake is concentrated on the former split tee. After the earthquake, the earthquake resistance of the building can easily be recovered by replacing the damaged split tee.
Furthermore, as the integrated effect of the above inventions, in the case where a large earthquake occurs for example, by making the portion of a split tee, to which a column and a beam are connected, yield in advance of the column and thus concentrating the damage at the split tee only, even when the portion of the split tee becomes unusable after the earthquake, the earthquake resistance of the building can be recovered by replacing the split tee. When an earthquake-resistant design is applied to a column and a beam, it is preferable in the design to make the beam (or split tee in the present invention) yield in advance of the column, but, since the design is usually implemented adopting the lower limit of the yield stress of a steel material as the proof stress of the design, the actual yield stress of the steel material is higher than the designed proof stress. Therefore, even though a load which is expected to cause yield in a design is imposed, there may be some cases where the portion does not yield. For instance, even though a structure is designed so as to make a split tee yield in advance of a column, if the yield stress of the steel material used for the split tee is higher than a designed proof stress, there may be some cases where the column yields in advance.
The present invention makes it possible to design a join wherein a split tee yields in advance of a column surely by regulating the upper limit of the yield stress of a steel material used for the split tee and defining the upper limit of the yield stress as the proof stress for designing. Further, the narrower the regulated range of the yield stress of a steel material is, the more the cross-sectional area of a column can be reduced and, therefore, an economical design can be realized.
Explanations will further be done referring to FIG. 18. FIGS. 18(a) to 18(c) show the relation between the stress ("sgr":N/mm2) and the strain (xcex5) with respect to the three kinds of steel materials which are assumed to be used for split tees.
FIG. 18(a) shows the case where a split tee produced from a conventional steel material (SS material: JISG3101, etc.) is used. In this case, if the lower limit of the yield stress ("sgr" min) of a steel material is defined to be the yield stress in design, as the upper limit of the yield stress ("sgr" max) is not regulated, it sometimes happens that a steel material having a very high yield stress is used and a column tends to yield in advance. In the case where an SN material (JISG3106) is assumed to be used for a split tee as shown in FIG. 18(b), the upper limit of the yield stress of the material is 1.35 to 1.5 times the lower limit of the yield stress. In the case where a steel material developed by the present inventors is used for a split tee as shown in FIG. 18(c), the upper limit of the yield stress of the material is 1.2 times the lower limit of the yield stress. In this case, the regulated range of the yield stress of the split tee is narrow and it is possible to make the split tee yield surely at the web or the flange thereof in advance of the column, and thus the effectiveness of the present invention is confirmed.
The portions of a split tee used in the present invention may be made of the same steel material having the same yield stress. However, to obtain the effect of the present invention, at least the web or the flange of a split tee may be made of a steel material having the material properties according to the preset invention.